1. Field of the Invention
The present invention relates to a driving apparatus of a liquid crystal display apparatus in which a plasma addressed liquid crystal display apparatus is used.
2. Description of the Related Art
Recently, after an installation space or the like which can be secured at home, for example, is taken into consideration, a large-sized and thin-type television image receiver and a back-projection type projector apparatus have been in common use in order to obtain a more forceful image.
According to technical progress, such a television image receiver and a back-projection type projector apparatus have been thinner compared with the conventional ones. However, there is a limit in their thinning because of structural conditions such as depth of a CRT (Cathode Ray Tube) of the television image receiver and installation angle of a projection lens of the projector apparatus.
In addition, a display device using a TFT (Thin Film Transistor) liquid crystal panel can be thinned further than the above-mentioned television image receiver and the protector apparatus. However, in order to produce a large-sized display apparatus, according to increase in number of TFTs formed by IC technique, more accurate producing technique is required, and the cost becomes very high due to decrease in the yield of production.
Therefore, there has been proposed a display device using a plasma addressed liquid crystal display apparatus (hereinafter, referred to as PALC from its initial), where a screen which is as large as those of the television image receiver and projector apparatus is formed and which is as thin as the TFT liquid crystal panel, as a display section.
Such a plasma addressed liquid crystal display apparatus can realize high luminance and high contrast which are as high as those of the TFT liquid crystal panel, and can realize a large screen by means of producing technique of a PDP (Plasma Display Panel). Moreover, the plasma addressed liquid crystal display apparatus is a normally white (or normally black) plasma addressed liquid crystal display apparatus.
There will be described below a structure of a PALC to be used in embodiments of the present invention, mentioned later, with reference to FIGS. 2 and 3. FIG. 2 is an exploded perspective view of a liquid crystal display apparatus using the PALC. FIG. 3 is a perspective view showing a part of the structure of the PALC, and shows a cross section of the part. As shown in FIG. 2, a PALC 1 has a structure of a transmitting display device where a luminous flux radiated from a back light 2 arranged on a rear surface of the PALC 1 is selectively transmitted by an active-matrix method, and thus an image is formed.
As shown in FIG. 3, a plasma substrate (rear glass) 5 is formed with scanning grooves 7, 7, 7, . . . which are partitioned with an uniform interval into a hollow shape in a horizontal direction, for example, (or scanning grooves which are formed by cutting) by partition walls 6, 6, 6, . . . Anode electrodes 8, 8, 8, . . . and cathode electrodes 9, 9, 9, . . . are formed respectively in the scanning grooves 7 with an uniform interval so as to make a pair. Namely, the scanning grooves 7 compose horizontal scanning lines corresponding to an effective screen of the PALC 1, and the scanning grooves 7 are formed correspondingly to a number of the scanning lines (for example, about 480 lines).
A thin glass substrate 10 forming an insulating layer is provided on the forward side of ribs 6, 6, 6, . . . so that the scanning grooves 7 can be sealed. A noble gas such as a helium gas or a mixed gas of noble gases is charged as a plasma gas into the scanning grooves 7.
In addition, an about -300 V scanning voltage of a negative polarity pulse, for example, is applied from a driver circuit of plasma discharge, not shown, to the cathode electrodes 9 with a predetermined timing (here, a ground electric potential is given to the anode electrodes 8), and as detailed later, a plasma discharge takes place between the anode electrodes 8 and the cathode electrodes 9.
Due to this plasma discharge, the plasma gas is ionized in the scanning grooves 7, and electrically conductive bodies, namely plasma channels are formed until the plasma particles completely vanish so that a selecting operation (strobe) which is equivalent to that of a switching element is performed.
On the front side of a thin plate glass substrate 10, a liquid crystal layer 11 for forming an image in a matrix pattern, color filters 12 which are composed of striped red, green and blue filter sections 12R, 12G and 12B corresponding to the colors of red, green and blue, transparent driving electrodes (as one example, ITO (Indium Tin Oxide) thin films) 13 which are composed of striped red, green and blue driving electrodes 13R, 13G and 13B for driving pixels of the liquid crystal layer 11 are arranged with an uniform interval so as to intersect perpendicularly to the scanning grooves 7, 7, 7, . . . Each of the intersected portions becomes each of the pixels.
Namely, an image signal (data) for one horizontal line amount is supplied to the transparent driving electrodes 13R, 13G and 13B of the PALC 1, and the plasma gases in the scanning grooves 7 are selected (strobe) in a vertical direction successively so as to be discharged. As a result, the image signal is applied to the liquid crystal of the pixels where the transparent driving electrodes 13R, 13G and 13B intersect perpendicularly to the scanning grooves 7, and transmittance of a light emitted from the back light 2 is different at each of the pixels so that a color image can be displayed.
Namely, as shown in FIG. 2, when polarization filters 3 and 4 are arranged respectively on an incident side and an emission side of the PALC 1, a quantity of transmitted light polarized by the PALC 1 can be controlled. As a result, a color image can be obtained by a principle which is similar to that of a normal TFT liquid crystal display apparatus.
Detailed below is the switching operation for forming an image for 1 field amount with reference to FIGS. 4 and 5. FIG. 4 is a schematic diagram showing a portion of the PALC 1 shown in FIG. 3 viewed from the side. Here, in order to explain the switching operation by means of plasma channels, for convenience, a switch SW is shown in FIG. 5A.
As mentioned above, when a plasma generating pulse of -300 V, for example, is applied to the cathode electrodes 9 (a ground electric potential is given to the anode electrodes 8) so that plasma discharge is caused, plasma channels are formed in the scanning grooves 7. The plasma channels become virtual electrodes so that an image signal voltage is applied between the transparent driving electrode layers 13 (red, green and blue driving electrodes 13R, 13G and 13B) and the anode electrodes 8.
FIG. 4 shows a state that when the voltage of -300 V is applied to the cathode electrode 9 by the switch SW, the plasma gas is generated by discharge in the scanning groove 7 on the first line, and the strobe is turned ON. The plasma gas is not yet generated in the scanning groove 7 on the second line, and the strobe is remained OFF. As shown in FIG. 4, when the plasma channels are formed by the plasma discharge, the inside of scanning grooves 7 is in a conducting state, and this, as shown in FIG. 5B, can be equivalently explained as an operation of an FET (Field-effect Transistor) switching element.
This switching operation by means of the plasma channels generates a virtual electrode on an inner surface of the thin glass (substrate) 10 in FIG. 4. Here, when an image signal voltage for driving pixels is applied to the transparent driving electrodes 13R, 13G and 13B, a driving voltage is applied to the respective pixels (for 1 line amount) of the liquid crystal layer 11 which become the intersections between the scanning grooves 7 where plasma discharge is taking place and the transparent driving electrodes 13R, 13G and 13B.
Therefore, scanning is executed so that the plasma discharge takes place in the scanning grooves 7 successively (for example, on the first through 480th lines), and an image of 1 field, for example, is formed. As a result, the image for 1 field amount can be displayed.
Namely, after selection is made as to an image on which line is formed by the plasma channel, a driving voltage for forming the image on that line is applied to the red, green and blue driving electrodes 13R, 13G and 13B so that the selective scanning of the line composing one field is realized. At this time, a light transmitted through the liquid crystal layer 11 is transmitted through the red, green and blue filter sections 12R, 12G and 12B of the color filter 12 so that a color image can be displayed. As a result, the driving voltage is applied successively to the cathode electrodes on the 1st through 480th lines synchronously with the driving of the pixels for 1 line so that an image for 1 field amount can be formed.
When the display device is composed by using a PALC which can form an image by means of such a structure and operational principle, a thin and light display device having a large screen can be constituted.
There will be detailed below concrete circuits of the driving apparatus of the liquid crystal display apparatus device having the conventional plasma addressed liquid crystal display apparatus with reference to FIG. 20. In FIG. 20, a broadcasting receiving means such as an NTSC-system U/V tuner or a BS tuner, not shown, and one or plural input terminals for inputting a standard video signal reproduced by an external equipment such as a VTR or the like are provided at the previous stage of an NTSC (National Television System Committee) demodulating section 21.
The standard video signal selected by the broadcasting receiving means and external standard video signal(s) input from the one or plural input means are selected in the display device and then supplied to the NTSC demodulating section 21.
The NTSC demodulating section 21 demodulates the standard video signal into a brightness signal and a color-difference signal, and the brightness signal and the color-difference signal are supplied to a double speed converting section 22. Moreover, the demodulating section 21 extracts a synchronizing signal from the demodulated brightness signal so as to supply the synchronizing signal to a LCD (Liquid crystal display apparatus) controller 28, mentioned later. Operating clocks of respective function circuits, mentioned below, are generated in the LCD controller 28 so that various signal processes are synchronized.
A frame memory which can store an image signal brightness signal and color-difference signal) for 1 frame amount thereinto is provided in the double speed converting section 22, and a motion component is detected by utilizing the frame memory. In a static image area of the image signal written into the frame memory, an image signal for 1 horizontal period in a field at that time and 1 field previous to that field is read out two times continuously with a speed twice as fast as a writing speed.
In addition, in a dynamic image area of the image signal written into the frame memory, an interpolating image signal, which is generated by an interpolation process by means of an image signal for 1 horizontal period of field information at that time and image signals for one up and down horizontal periods, is read out with a doubled speed, and the interpolating image signal is converted into a non-interlace signal of 525 H/60 Hz.
After the image signal which was subjected to the double speed process undergoes color adjustment, hue adjustment and the like in an image signal processing section 23, primary-colors signals of red, green and blue are generated by a matrix process. The respective primary-colors signals generated in the image signal processing section 23 are subject to gain adjustment by a gain regulator 24 for adjusting gain according to a control signal from a micro computer control section 33 and then supplied to an A/D converter 25 having 8-bit quantizing accuracy. Then, the primary-colors signals are converted into red, green and blue digital image data V8 therein. The gain regulator 24 reduces a level of an input signal to be supplied to the A/D converter 25 and reduces a number of gray scales of the image data to be displayed. As a result, a driving voltage to the transparent electrodes 13 is lowered, and thus the contrast is reduced.
The red, green and blue image data V8 obtained by the A/D converter 25 are subject to a white balance process in a white balance regulating section 26 and then supplied to a liquid crystal column driver 27.
The liquid crystal column driver 27 latches image data for 1 horizontal period (for example, 854 pixels), namely image data V8 of 854 pixels.times.3 channels (red, green, blue), namely, 2562 pixels, and holds the image data V8 for each pixels for 1 horizontal period. When the plasma discharge is generated in the predetermined scanning groove 7 (FIG. 3) by a plasma driver 31, mentioned later, the image data V8 are read out per 1 horizontal line. The image data V8 are converted into analog signals by a D/A converter provided in the liquid crystal column driver 27 and then applied to the transparent driving electrodes (ITO) 13 (red, green and blue driving electrodes 13R, 13G and 13B) (FIG. 3) of a PALC (plasma addressed liquid crystal display apparatus) 36 (1).
The LCD controller 28 is composed :so as to be operated by a power supply of 5V, for example. The LCD controller 28 generates an anode inversion pulse (H pulse), for driving an anode inversion driving circuit 30, and a plasma pulse, for driving a plasma driver 31 so that the plasma discharge takes place per scanning groove 7 (horizontal line), based on an operating clock-generated based on the synchronizing signal from the NTSC demodulating section 21.
A reference voltage VREF from a reference voltage generating circuit 29 is applied to the liquid crystal column driver 27 containing a charge and hold type D/A converter, mentioned later so as to drive the transparent driving electrodes 13 of the PALC 36 (1). Moreover, an anode driving voltage from the anode inversion driving circuit 30 is applied to the anode electrodes 8 of the PALC 36 (1).
The plasma driver 31 successively selects horizontal scanning lines corresponding to about 480 lines composing an NTSC screen, namely, the scanning grooves 7 formed in the PALC 36 (1) as shown in FIG. 3 so as to supply plasma pulses, and allows the plasma discharge to take place according to the power-supply voltage of about -300 V applied to the cathode electrodes 9.
In other words, plasma discharge occurs in the scanning grooves 7, 7, 7, . . . successively from, for example, the top to the bottom in synchronization with the image data V8 with the doubled speed inputted into the liquid crystal column driver 27, and the discharge state is repeated per field so that the PALC 36 (1) can be driven according to the image data mentioned above. As a result, the inputted standard video signal can be displayed as an image.
As shown in FIG. 2, a back light 35 (2) is provided as a light source for illuminating the PALC 36 (1) from the back side. The luminous flux emitted from the back light 35 (2) transmits through predetermined pixels of the PALC 36 (1) so that a display image is formed. Moreover, the brightness of the back light 35 (2) is adjusted so that a picture can be adjusted.
The micro computer control section 33 makes various controls such as selection of the tuners, the adjustment of an image and on/off operation of the power supply or the like according to commands inputted by a user using an operating section 32. Here, in FIG. 20, an object to be controlled by the micro computer control section 33 and the micro computer control section 33 are connected with each other by a broken line.
In the driving apparatus of the liquid crystal display apparatus having the conventional plasma addressed liquid crystal display apparatus described with reference to FIG. 20, when the gain regulator 24 lowers a level of the input signal to be supplied to the A/D converter 25 and reduces a number of gray scales of image data to be displayed, a driving voltage for driving the transparent electrodes 13 is lowered so that the contrast is reduced.
At this time, for example, at the minimum point of the contrast adjustment, the level of the input signal is reduced by about 25%, namely, reduced to about 1/4+L . However, as a result, 256 (8 bits) gray scales of a driving voltage becomes about 64 (6 bits) gray scales, and thus there arises a problem that S/N of the display image is lowered.